JPH02173931A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To stably coat upper layers of a medium when the lower layer is formed by extrusion coating method by continuously adding a hardening agent to the coating liquid at a proper amt. to the amt. of the magnetic coating liquid to be applied on the substrate. CONSTITUTION:The coating liquid is continuously supplied from a tank 1 by a pump 4 to a mixer 6 at a proper amt. for coating, while the hardening agent is continuously supplied from the tank 2 at a proper amt. to harden to magnetic coating liquid. The two liquids are stirred and mixed in the mixer 6 and continuously sent to a head 3 for extrusion coating to be applied on a running substrate 7. By this method, the magnetic coating liquid is applied on the substrate immediately after mixed with the hardening agent, so that the mixed liquid has constant viscosity. Thereby, coating of upper layers can be always performed in a stable state.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method of manufacturing a magnetic recording medium,
More specifically, the present invention relates to a method for manufacturing a magnetic recording medium using a wet multilayer coating method, which is a so-called wet-on-wet coating method, in which a plurality of coating liquids are applied on a flexible support in a superimposed manner in a wet state.

[Background of the Invention] Magnetic recording media are generally manufactured by using a magnetic coating liquid containing magnetic powder, a binder resin, a dispersant, a lubricant, and other additives mixed and dispersed, and then hardened to improve the durability of the magnetic layer. It is manufactured by adding the agent, coating it on a support, and drying it.

Conventionally, methods such as roll coating, gravure coating, and extrusion coating have been commonly used as multilayer coating methods for magnetic coating liquids. The uniformity of the thickness is poor, especially when the wet-on-wet method is applied, and when the lower layer is formed by roll coating or gravure coating, as the upper layer becomes thinner, the uneven thickness of the lower layer becomes more This affects the coating and also has an adverse effect on the performance of the magnetic recording medium. For example, a decrease in its electromagnetic conversion properties occurs.

On the other hand, when the lower layer is formed by extrusion coating, the uniformity of the film thickness is excellent, so even if the upper layer becomes thin, the coatability of the upper layer is not affected. A method of adding a curing agent in an amount commensurate with the amount of the coating liquid used for the second coating operation, and then starting the coating operation (in the present invention, the addition of the curing agent to the magnetic coating liquid is performed in this way). (This method is called the off-line curing agent addition method.) If the coating operation is performed for a long time, the coating liquid to which the curing agent has been added is left in the coating liquid tank for a long time, which causes the viscosity of the coating liquid to increase. As a result, the optimum conditions for coating the upper layer change, making it impossible to coat the upper layer stably.

[Object of the Invention] The present invention aims to correct these drawbacks.

That is, when the lower layer is formed by the extrusion coating method, even if coating is performed for a long time, the coating state of the lower layer (in other words, the viscosity state of the coating liquid discharged from the extrusion coating head does not change); The object of the present invention is to provide a method by which the upper layer can be applied stably.

[Structure of the Invention] The object of the present invention is to add the curing agent not by the offline addition method as described above, but by adding it in the process of continuously applying the magnetic coating liquid onto the moving support. , a method in which a hardening agent is continuously added to the coating solution in an amount corresponding to the amount of the magnetic coating solution to be coated on the support (hereinafter, in the present invention, in the process of such continuous coating,
A method in which a hardening agent is continuously added to a magnetic coating liquid is called an in-line hardening agent addition method. ) That is, the present invention provides a method for manufacturing a magnetic recording medium comprising a plurality of layers coated on a flexible support, in which the plurality of layers are coated with an extrusion type coating head. A method for producing a magnetic recording medium, which is formed in a wet state in a superimposed manner, and at least the layers other than the top layer are coated with a coating liquid using an in-line hardening agent addition method. It is.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings, while comparing it with an offline curing agent addition method.

FIG. 1 is a process diagram showing an outline of the production of a magnetic coating liquid by an offline hardening agent addition method, and FIG. 2 is a process diagram showing an outline of magnetic liquid manufacturing by an inline hardening agent addition method of the present invention.

In Figures 1 and 2, ■ indicates a magnetic coating liquid tank, 2
3 is a hardening agent tank, 3 is an extrusion type coating head, 4 is a magnetic coating liquid feeding pump, 5 is a hardening agent liquid feeding pump, 6 is a mixer (Figure 2 only), 7 is a rain coating for a traveling support. .

First, to explain one aspect of the method of coating a magnetic coating liquid onto a support produced by the off-line curing agent addition method shown in Fig. 1, the total amount of magnetic coating liquid used for one coating operation is placed in a magnetic coating liquid tank l. (excluding curing agent component),
A curing agent component is charged into the curing agent tank 2 (if the curing agent component is solid, an inert liquid diluent is added to the curing agent to make it liquid). Next, prior to the coating operation, an amount of curing agent corresponding to the amount of magnetic coating liquid charged in tank 1 is sent from tank 2 to tank 1 by pump 5, and both are stirred and mixed in the tank.

When applying the magnetic coating liquid produced in this way onto the support 7, the magnetic coating liquid in the tank 1 is continuously supplied to the extrusion type coating head 3 by the pump 4, and the magnetic coating liquid is supported while the support body 7 is being moved by the head. The magnetic coating liquid is continuously applied to the body 7.

However, when continuous coating is performed for a long time using this method, the magnetic coating liquid to which a hardening agent has already been added is left in the tank for a long time, resulting in the viscosity of the liquid changing over time. The viscosity state of the coating layer also changes over time.

For this reason, when a wet-on-wet multilayer coating is performed on a lower layer formed by such a method, there is a drawback that the upper layer cannot be coated in a stable manner, as described above.

Next, referring to FIG. 2, we will explain how to apply the magnetic coating liquid produced by the in-line curing agent addition method of the present invention onto a support. First, as in the case of FIG. Pour the entire amount of the magnetic coating liquid (excluding the curing agent component) used in the work, and charge the curing agent component into the curing agent tank 2 (if the curing agent component is solid, add an inert agent to the curing agent as appropriate). Add a liquid diluent to make it liquid).

Next, when applying the magnetic coating liquid to the support 7, the magnetic coating liquid corresponding to the coating amount is continuously supplied from the tank 1 to the mixer 6 by the pump 4, and the magnetic coating liquid is supplied from the convenience agent tank 2 to the mixer 6. The amount of curing agent required for curing is continuously supplied to the mixer 6.

The magnetic coating liquid and curing agent liquid continuously supplied to the mixer 6 are stirred and mixed in the mixer 6, and the obtained magnetic coating liquid is continuously supplied to the extrusion type coating head 3. It is applied onto the supporting body 7 while it is running.

The magnetic coating liquid produced by this method is coated onto the support by an extrusion coating head immediately after the curing agent is added, so that the viscosity of the constituent liquid is always constant.

Therefore, even when multi-layer coating is performed on the constituent layers by the wet-on-wet method, the same troubles as in the case of magnetic coating liquids manufactured by the off-line curing agent addition method for coating the upper layer are not observed. , can always be performed in a stable state.

The mixer 6 used in the present invention is, of course, not limited to the type shown in FIG. For example, a so-called pipe mixing device (machine) that can stir and mix two fluids in a pipe is also suitably used as the mixer 6.

It is preferable to use a metering pump for each of pumps 4 and 5, and if necessary, each pump is equipped with a flow meter, an automatic flow rate regulator, etc. to adjust the flow rate as necessary to maintain a constant flow rate. It is desirable to be able to obtain

In the present invention, when applying a magnetic coating liquid to a support using an extrusion type head or the like to form a plurality of constituent layers in a wet state by overlapping each other, at least the layers other than the top layer are formed using an in-line curing agent addition method. Although it is necessary that the uppermost layer be coated with a magnetic coating liquid manufactured by the above-mentioned method, it is also possible to coat the uppermost layer using a magnetic coating liquid manufactured by an in-line curing agent addition method.

The amount of coating liquid for the uppermost layer is usually preferably 257 or less.

Regarding the magnetic coating liquid used in the present invention, the magnetic coating liquid and its manufacturing technology conventionally used for this type of magnetic recording medium can be directly used.

Examples of the magnetic material used in the present invention include γ-Fe
20. , Co-containing-Fe20. or CO deposited-F
e, O.

CO-γ-Fe, O,, Fe, 0. , Co-containing Fe, O, or Co-coated Fe, O,
-Fe2O3; Oxide magnetic materials such as CrO2, others such as Fe, Ni, Fe-Ni alloy, Fe-Co alloy, Fe-N1-P alloy, Fe-N1-Co alloy, Fe
-Mn-Zn alloy.

Fe-Ni-Zn alloy, Fe-Co-Ni-Cr alloy,
Fe-Go-Ni-P alloy.

Examples include various ferromagnetic materials (powders) such as metal magnetic powders containing Fe, Ni, and Co as main components, such as Go-P alloys and Go-Cr alloys. Additives to these metal magnetic materials may include elements such as Si, Cu, Zn, AQ, P, Mn, and Cr, or compounds thereof. Hexagonal ferrite such as barium ferrite, iron nitride, etc. are also used.

The binder used in the present invention includes abrasion-resistant polyurethane. It has strong adhesion to other substances, is mechanically strong to withstand repeated stress or bending, and has good abrasion resistance and weather resistance.

Furthermore, if a cellulose resin and a vinyl chloride copolymer are used in combination with polyurethane, the dispersibility of the magnetic powder in the magnetic layer will be improved and its mechanical strength will be increased. However, if only the cellulose resin and the vinyl chloride copolymer are used, the layer becomes too hard, but this can be prevented by the presence of the above-mentioned polyurethane.

Phenoxy resins can also be used.

Phenoxy resin has advantages such as high mechanical strength, excellent dimensional stability, good heat resistance, water resistance, chemical resistance, and good adhesiveness.

These advantages are complementary to those of the polyurethane described above, and the stability of the physical properties of the tape over time can be significantly improved.

Furthermore, in addition to the binders described above, mixtures of thermoplastic resins, thermosetting resins, reactive resins, and electron beam curable resins may be used.

In order to improve the durability of the magnetic layer of the magnetic recording medium of the present invention, the magnetic paint can contain various curing agents, such as incyanate. Examples of aromatic isocyanates include tolylene diisocyanate (TDI) and adducts of these isocyanates with active hydrogen compounds, with an average molecular weight of 100
A range of 3.000 to 3.000 is preferred.

Examples of aliphatic incyanates include hexamethylene diisocyanate (HMDI) and adducts of these incyanates and active hydrogen compounds. Among these aliphatic incyanates and adducts of these isocyanates and active hydrogen compounds, those having a molecular weight in the range of 100 to 3,000 are preferred. Among the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred.

A dispersant is used in the magnetic coating liquid of the present invention, and additives such as a lubricant, an abrasive, a matting agent, an antistatic agent, etc. may be included as necessary. Dispersants used in the present invention include phosphoric acid esters, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinic esters,
There are known surfactants and their salts, and salts of polymer dispersants having negative organic groups (for example, -〇〇〇H) can also be used. These dispersants may be used alone or in combination of two or more.

In addition, as lubricants, silicone oil, gelaphalite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid, monobasic fatty acids with 12 to 16 carbon atoms and carbon atoms of the fatty acids are used. Fatty acid esters (so-called waxes) consisting of monohydric alcohols having a total of 21 to 23 carbon atoms can also be used. These lubricants are added in an amount of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

As the abrasive, commonly used materials such as fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, artificial diamond, garnet, and emery (main components: corundum and magnetite) are used. These abrasives have an average particle diameter of 0.05 to 5μ, and
Particularly preferably, it is 0.1 to 2 μm. These abrasives are added in an amount of 1 to 20 parts by weight based on 100 parts by weight of the binder.

As the matting agent, organic powder or inorganic powder may be used individually or in combination.

As the organic powder used in the present invention, acrylic styrene resin, benzoguanamine resin powder, melamine resin powder, and phthalocyanine pigment are preferable, but polyolefin resin powder, polyester resin powder, polyamide resin powder, and polyimide resin are preferred. Powder, polyfluoroethylene resin powder, etc. can also be used, and inorganic powders include silicon oxide, titanium oxide, aluminum oxide, calcium carbonate,
barium sulfate, zinc oxide, tin oxide, aluminum oxide,
Chromium oxide, silicon carbide, calcium carbide, α-Fe20
1, talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, and molybdenum dioxide.

Antistatic agents include carbon black, graphite, conductive powders such as tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds; natural surfactants such as saponin; alkylene oxides, and glycerin. Cationic surfactants such as higher alkylamines, quaternary ammonium salts, pyridine, other heterocycles, phosphoniums or sulfoniums; Carboxylic acids, sulfonic acids, phosphoric acids, sulfuric acids Anionic surfactants containing acidic groups such as ester groups and phosphate ester groups; amino acids;
Examples include amphoteric activators such as aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, and the like.

Solvents to be added to the above paint or diluting solvents during application of this paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol, ethanol, propatool, and butanol; , esters such as ethyl acetate, butyl acetate, ethyl lactate, and ethylene glycol monoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, and tetrahydrofuran; aromatic hydrocarbons such as benzene, toluene, and xylene; methylene chloride , ethylene chloride, carbon tetrachloride, chloroform, dichlorobenzene, and other halogenated hydrocarbons.

In addition, as a support, polyethylene terephthalate,
Examples include polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. Metals such as Zn, glass, boron nitride, ceramics such as Si carbide, etc. can also be used.

The thickness of these supports is approximately 3 to 100 μm in the case of a film or sheet, preferably 5 to 50 μm.
In the case of a disk or card shape, the thickness is about 30 μm to 10+a+m, and in the case of a drum shape, it is used in a cylindrical shape, and the shape is determined depending on the recorder used.

An intermediate layer for improving adhesion may be provided between the support and the magnetic layer.

Coating methods for forming the magnetic layer on the support include air knife coating, blade coating, air knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, Although spray coating, extrusion coating, etc. can be used, in the present invention, an extrusion coating method is particularly used as described above.

By such a method, the magnetic layer coated on the support is optionally treated to orient the ferromagnetic metal oxide powder in the layer, and then the formed magnetic layer is dried.

In this case, the orientation magnetic field is approximately 500 to 50
The drying temperature is approximately 50-120°C.
The drying time is approximately 0.5 to 10 minutes. Further, the magnetic recording medium of the present invention is manufactured by subjecting it to surface smoothing treatment or cutting it into a desired shape, if necessary.

Next, the present invention will be explained with reference to examples, but it goes without saying that the present invention is not limited to these examples.

[Example] Comparative Examples 1 to 2 and Example 1 Magnetic coating liquids having the compositions shown in Tables 1 to 2 were manufactured by an offline curing agent addition method and an inline addition method, respectively, and the obtained magnetic coating liquids were coated. By changing the method, the dry film thickness of the upper layer was 0.7μ11 and the dry film thickness of the lower layer was 3.3μ by wet-on-wet method on the moving support.
Multilayer coating of two layers (upper layer and lower layer) was performed under μm conditions.

Table 3 shows the hardening agent addition method and coating method for the magnetic coating liquid used.

Table 1 Table 2 Table 3 The results of measuring the electromagnetic conversion characteristics of the magnetic recording media thus manufactured are shown in Table 4 below.

In the case of Comparative Example 2 in Table 4, the electromagnetic wave conversion characteristics of the magnetic recording medium immediately after the start of coating are as good as in Example 1 according to the present invention, but as the coating time becomes longer, the electromagnetic conversion characteristics of the magnetic recording medium Furthermore, when coating was started 20 minutes after preparing the magnetic liquid for coating, the thickness of the upper layer became thicker after 2 hours, and slight coating unevenness occurred. .

On the other hand, in the case of Example 1 according to the present invention, no such troubles were observed and stable coating could be performed for a long time.

[Effects of the Invention] According to the present invention, a magnetic coating liquid having a constant viscosity can be extruded onto a support from an extrusion coating head.

Therefore, even when multilayer coating is performed by wet-on-wet method on the constituent layers coated by the method of the present invention, the upper layer can be coated in a stable state.

In addition, when extrusion is applied in multiple layers using a coating head using a magnetic coating liquid manufactured by the conventional off-line curing agent addition method, the coating amount of the upper layer is limited because the coating condition of the lower layer changes. The amount is approximately 2
If the coating amount is less than 5+aQ/m", uneven coating will occur, but according to the present invention, since the coating condition of the lower layer is constant, uneven coating will occur even if the coating amount of the upper layer is less than 25 mff/m". It is advantageous because there are no problems.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an outline of a method for producing a magnetic coating liquid using a conventional off-line hardening agent addition method, and FIG. 2 is a diagram showing a method for manufacturing a magnetic coating liquid using an in-line hardening agent addition method. Magnetic coating liquid tank Hardener tank Extrusion type coating head Magnetic coating liquid feed pump Hardener liquid feed pump Mixer support

Claims (2)

[Claims] (1) In a method for manufacturing a magnetic recording medium comprising a plurality of layers coated on a flexible support, the plurality of layers are formed by superimposing them in a wet state using an extrusion type coating head, and at least A method for producing a magnetic recording medium, characterized in that layers other than the upper layer are coated with a coating liquid prepared by an in-line curing agent addition method. (2) The method for manufacturing a magnetic recording medium according to claim (1), wherein the uppermost layer is coated with a coating liquid prepared by an in-line curing agent addition method.